A blockchain is a publicly viewable, append-only, distributed ledger. A conventional blockchain includes multiple blocks, each containing data and a hash of the previous block, thereby linking the blocks in the blockchain. Blockchain entries consist of blocks of information that can include financial and other types of transactions, data records, and other information, such as timestamps. An example of a trusted timestamp is a timestamp that incorporates a time stamp token (TST). As an example, trusted timestamps can be defined according to the X.509 Public Key Infrastructure Time-Stamp Protocol (RFC 3161) specification.
Blockchains can be permissionless or permissioned. A permissionless blockchain is one in which identity of participants is anonymous or pseudonymous. Transactions are processed through a proof-of-work consensus mechanism in which participants agree that the fork with the lengthiest proof of work behind it at a given time is deemed the correct fork.
A permissioned blockchain is one in which participant identities must be authorized to contribute to validating transactions. Permissioned blockchains can utilize various consensus mechanisms, such as proof-of-stake. Because participants in a permissioned blockchain are known and vetted, the consensus mechanism of permissioned blockchains can be much less computationally-intensive than that of permissionless blockchains.